1. Field
The present application relates generally to wireless communications, and more specifically to techniques for adapting to interference in spectrums shared by WAN macro cells and femto cells.
2. Background
Wireless communication systems are widely deployed to provide various types of communication (e.g., voice, data, multimedia services, etc.) to multiple users. As the demand for high-rate and multimedia data services rapidly grows, there lies a challenge to implement efficient and robust communication systems with enhanced performance.
In recent years, users have started to replace fixed line communications in their homes and offices with mobile communication devices, and a new class of small base stations has emerged, which may be installed in homes and offices to provide better indoor wireless coverage to mobile units. Such personal miniature base stations are generally known as femto access points, access point (AP) base stations, Home Node B (HNB), or Femto cells. Typically, such miniature base stations are connected to the Internet and the mobile operator's network via a digital subscriber line (DSL) router or cable modem.
Femto cells allow for cellular access where normal base station support is weak or unavailable (e.g., indoors, remote locations, and the like). Femto cells may be described as small base stations that connect to wireless service providers via a broadband backhaul link, such as DSL, cable internet access, optical fiber, T1/T3, etc., and offer typical base station functionality, such as base transceiver station (BTS) technology, radio network controller, and gateway support node services. This allows cellular devices to connect to the femto cells and utilize the wireless service. Femto cells provide significant capacity benefits and improved user experience.
Sometimes, femto cells and wide area network (WAN) macro cells share the same cellular spectrum, which may result in signal interference. Interference issues are further exacerbated by the fact that femto cells may restrict which nodes can and cannot connect to it. For example, the owner of a femto cell may want to limit its use to a set of users that he/she defines. This is in contrast to conventional cellular system wherein a user with a subscription can connect to any base station, preferably the best RF link, deployed by the operator. Such femto cells are sometimes referred to as restricted association or closed subscriber group femto cells. For example, a femto access point (AP) may be trying to serve a femto access terminal (AT) (e.g., in a femto user's house), when a WAN AT, that is restricted from accessing that Femto, comes near the femto AP/AT. The femto cell becomes susceptible to interference when the WAN AT communicates with the WAN network near the femto AP/AT, such as, for example, when a visitor to the user's house tries to make a call using his/her mobile phone. The interference may particularly affect the femto cell on certain bandwidth portions of the shared spectrum dynamically based on the scheduling actions of the WAN AP. Accordingly, there is a need for a technique to mitigate the effects of such interference associated with such bandwidth portions of the spectrum.